Explaining Entropy responses after a noxious stimulus, with or without neuromuscular blocking agents, by means of the raw electroencephalographic and electromyographic characteristics.
ABSTRACT Entropy™, an anaesthetic EEG monitoring method, yields two parameters: State Entropy (SE) and Response Entropy (RE). SE reflects the hypnotic level of the patient. RE covers also the EMG-dominant part of the frequency spectrum, reflecting the upper facial EMG response to noxious stimulation. We studied the EEG, EMG, and Entropy values before and after skin incision, and the effect of rocuronium on Entropy and EMG at skin incision during sevoflurane-nitrous oxide (N₂O) anaesthesia.
Thirty-eight patients were anaesthetized with sevoflurane-N₂O or sevoflurane-N₂O-rocuronium. The biosignal was stored and analysed off-line to detect EEG patterns, EMG, and artifacts. The signal, its power spectrum, SE, RE, and RE-SE values were analysed before and after skin incision. The EEG arousal was classified as β (increase in over 8 Hz activity and decrease in under 4 Hz activity with a typical β pattern) or δ (increase in under 4 Hz activity with the characteristic rhythmic δ pattern and a decrease in over 8 Hz activity).
The EEG arousal appeared in 17 of 19 and 15 of 19 patients (NS), and the EMG arousal in 0 of 19 and 13 of 19 patients (P<0.01) with and without rocuronium, respectively. Both β (n=30) and EMG arousals increased SE and RE. The δ arousal (n=2) decreased both SE and RE. A significant increase in RE-SE values was only seen in patients without rocuronium.
During sevoflurane-N₂O anaesthesia, both EEG and EMG arousals were seen. β and δ arousals had opposite effects on the Entropy values. The EMG arousal was abolished by rocuronium at the train of four level 0/4.
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ABSTRACT: Major clinical endpoints of general anesthesia, such as the alteration of consciousness, are achieved through effects of anesthetic agents on the central nervous system, and, more precisely, on the brain. Historically, clinicians and researchers have always been interested in quantifying and characterizing those effects through recordings of surface brain electrical activity, namely electroencephalography (EEG). Over decades of research, the complex signal has been dissected to extract its core substance, with significant advances in the interpretation of the information it may contain. Methodological, engineering, statistical, mathematical, and computer progress now furnishes advanced tools that not only allow quantification of the effects of anesthesia, but also shed light on some aspects of anesthetic mechanisms. In this article, we will review how advanced EEG serves the anesthesiologist in that respect, but will not review other intraoperative utilities that have no direct relationship with consciousness, such as monitoring of brain and spinal cord integrity. We will start with a reminder of anesthestic effects on raw EEG and its time and frequency domain components, as well as a summary of the EEG analysis techniques of use for the anesthesiologist. This will introduce the description of the use of EEG to assess the depth of the hypnotic and anti-nociceptive components of anesthesia, and its clinical utility. The last part will describe the use of EEG for the understanding of mechanisms of anesthesia-induced alteration of consciousness. We will see how, eventually in association with transcranial magnetic stimulation, it allows exploring functional cerebral networks during anesthesia. We will also see how EEG recordings during anesthesia, and their sophisticated analysis, may help corroborate current theories of mental content generation.Clinical EEG and neuroscience: official journal of the EEG and Clinical Neuroscience Society (ENCS) 01/2014; · 3.16 Impact Factor
Article: Abstracts.Acta Anaesthesiologica Scandinavica 03/2013; · 2.36 Impact Factor
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ABSTRACT: Dexmedetomidine has been shown to blunt the stress response to surgery. Hence a study was designed to evaluate the effect of intravenous (IV) Dexmedetomidine infusion during general anesthesia for abdominal surgeries on blood glucose levels and on Sevoflurane requirements during anesthesia. Forty patients scheduled for abdominal surgery under general anesthesia were divided into Dexmedetomidine (D) group and Placebo (P) group of 20 each. Group D received a loading dose of Inj. Dexmedetomidine at 1 μg/kg/10 min diluted to 20 mL, followed by maintenance with 0.5 μg/kg/h., till the end of surgery. Group P received similar volume of IV normal saline. Anesthesia was maintained with nitrous oxide in oxygen and Sevoflurane keeping entropy between 40 and 60. Data were analyzed using students t test, chi square test and Fisher Exact test as applicable. During the first postoperative hour, Dexmedetomidine group showed blood glucose levels of 118.2 ± 16.24 mg/dL, compared to placebo group which was 136.95 ± 19.76 mg/dL and it was statistically significant (P < 0.01). Mean hourly Sevoflurane requirement in Group D was 11.10 ± 2.17 mL, compared to 15.45 ± 3.97 mL in placebo group. In peri-operative period, the heart rate and MAP were significantly lower in Group D, when compared to placebo. Patients in Group D were better sedated and post-operative pain score was better in Group D compared to Group P. IV Dexmedetomidine was effective in blunting stress response to surgical trauma as indicated by lower blood glucose levels, and reduces Sevoflurane requirements during entropy guided general anesthesia without affecting time for extubation.Journal of Anaesthesiology Clinical Pharmacology 01/2014; 30(1):25-30.